Rossdale operations

Screens are located just before the lowlift pumps to strain out debris which may enter the intake pipe. The screens are designed with small holes which keep out fish, sticks, and leaves. The screens are rotated and periodically cleaned using back-wash water to return debris to the river.

Alum and powdered activated carbon are the first chemicals added to the water. These chemicals are added by feed pumps which are adjustable to supply the correct dosages.

The lowlift pumps get their name because they pump at a high volume but at "low" pressure. They're approximately 1,000 horsepower and pump at a rate of 20 – 200 millions of litres per day (MLD).

When the chemicals are added, it is necessary to mix them thoroughly with the water. High intensity mixing is done at the lowlift pump station or in a mixing chamber.

Following rapid mix, polymer is added and the water is then slowly mixed to encourage the formation of floc. Floc (large jelly-like particles) results from the attraction of dirt particles to the chemicals alum and polymer. The floc later settles out of the water by gravity.

After the floc is formed, it is then allowed to settle to the bottom of a clarifying basin. This is the process of sedimentation. Once the dirt-laden floc settles to the bottom of the basin, sludge is removed and the clear water is decanted from the surface.

Free chlorine (0.8 % Sodium Hypochlorite) is added after clarification to kill harmful bacteria and other microbes. After filtration, the water passes through ultraviolet (UV) disinfection that renders the micro-organisms harmless. Ammonia is then added and combines with chlorine to form a long-lasting disinfectant called monochloramine.

The water is filtered by allowing it to slowly flow down through a layer of anthracite coal (about 50 cm) and a layer of sand (about 30 cm). The filters are regularly cleaned by pumping air and water back up through the sand and anthracite coal to dislodge any accumulated particles.

After filtration, the water goes into on-site reservoirs where it is stored until required. The reservoirs provide additional time for disinfection and also allow the treatment plant to handle variations in water demand throughout the day.

Highlift pumps get their name because they are required to pump water at “high” pressure. These pumps are each 2,000 horsepower and pump 100 MLD at a pressure of about 130 pounds per square inch (psi).

• 1947: Plant #1 was constructed​
  
• 1956: Plant #2 opened; designed for 250,000 people
• 1981-89: Plant was refurbished
• 2003: UV disinfection operational